Hydrofluoric acid (HF) is used as a catalyst in conventional industrial processes to perform reactions such as aromatic and olefin alkylation, including refinery processes for the production of high-octane gasoline, distillate, and lubricating base oil. The hazards of HF, e.g., related to HF volatility, are well documented. The use of additives to reduce HF volatility is expensive and does not eliminate the need for large quantities of HF in the plant. Meanwhile, efforts to develop safer, alternative catalysts have encountered serious challenges. The conversion of HF alkylation units to use sulfuric acid (H2SO4) as catalyst requires significant added capital and operating expense, and at the same time introduces the hazards associated with highly corrosive concentrated H2SO4. Further, solid alkylation catalysts have proved difficult to commercialize due to rapid fouling and deactivation.
FIG. 1 is a block diagram schematically representing an HF alkylation unit 10, according to the prior art. HF alkylation unit 10 may include a hydrocarbon feed line 13, an HF alkylation reactor 16 containing hydrocarbon injection nozzles, and an HF settler 18 coupled to HF reactor 16 for separating an HF/hydrocarbon mixture into a hydrocarbon phase and an HF phase. The HF phase may be recycled to HF reactor 16 via an HF heat exchanger 20. In a more compact design, the heat exchanger could be located inside the HF reactor.
A portion of the HF is sent to an HF regeneration unit 22, then the regenerated HF is combined with the HF recycle stream. Unit 10 may further include a fractionation unit 24 for fractionating the hydrocarbon phase, and a product treatment unit 26 for treating cuts from fractionation unit 24 to provide one or more products. In some instances, a prior art HF alkylation unit may include a feed treatment unit 12 for treating the hydrocarbon feed(s) to HF reactor 16.
U.S. Pat. No. 5,284,990 to Peterson et al. discloses a method for converting an HF alkylation unit to a H2SO4 alkylation unit. The disclosure of the '990 patent is incorporated by reference herein in its entirety for all purposes.
The quest for an alternative catalytic system to replace conventional HF and H2SO4 catalysts in alkylation processes has been researched by various groups in both academic and industrial institutions. Thus far, no viable replacement catalyst for performing such processes has been commercialized.
Recently there has been considerable interest in metal halide ionic liquid catalysts as alternatives to HF and H2SO4 catalysts. As an example, the ionic liquid catalyzed alkylation of isoparaffins with olefins is disclosed in U.S. Pat. No. 7,432,408 to Timken, et al. Further, U.S. Pat. No. 7,572,943 to Elomari, et al. discloses the ionic liquid catalyzed oligomerization of olefins and the alkylation of the resulting oligomers(s) with isoparaffins to produce alkylated olefin oligomers.
PCT Publication No. WO 2011/015664 discloses a method for revamping an HF or H2SO4 alkylation unit to an ionic liquid alkylation unit, wherein one or more cyclone units are provided to promote the separation of ionic liquid from hydrocarbons.
Liu et al. (Oil & Gas Journal (2006) Vol. 104, Issue 40) describe retrofitting an H2SO4 alkylation unit for use in composite ionic liquid catalyzed alkylation by modifying the settler internals to enhance the separation of the composite ionic liquid from alkylate gasoline, and by providing a surge tank, wherein the composite ionic liquid is recycled from the surge tank to a STRATCO® (continuous stirred tank) reactor.
There is a need for the efficient and cost-effective conversion of existing HF alkylation units into ionic liquid alkylation systems suitable for ionic liquid catalyzed alkylation processes.